The subject matter disclosed herein generally relates to engine systems for powering rotary winged aircraft. More specifically, the subject disclosure relates to exhaust systems for engines of rotary winged aircraft.
Typical rotary wing aircraft, such as helicopters, have one or more engines located at the airframe. These engines are connected to a rotor system, often via a gearbox. The engine produces exhaust, which is expelled from the aircraft via an exhaust duct.
In military aircraft gas turbine engines, it is highly desirable that infrared emissions from the engine be reduced to a practical minimum to avoid acquisition and tracking by heat seeking, hostile forces, or to permit effective countermeasures such as evasive action to be taken against such forces. Further, exhaust passageways are typically oriented to allow direct line of sight into the engine core. In helicopters, infrared suppression is typically achieved by directing the exhaust upwardly out of the airframe, via a duct with a bend in the duct to transfer the exhaust from a horizontal flow to a vertical flow. With such a configuration, the infrared signature is substantially blocked from below the aircraft and from behind the aircraft, and there is no direct line of sight into the engine core.
While the above configuration may have the desired effect on the infrared signature of the engine exhaust, the system inherently results in performance losses of both the engines and of the aircraft, as the force of the upwardly traveling exhaust acts opposite to the lift forces generated by the rotor system.